1. Field of the Invention
The present invention relates to a diamine compound having dendron side chains and an LC (liquid crystal) aligning agent using the same. More particularly, the present invention relates to an LC aligning agent in which shrub-shaped dendron side chains are introduced into a diamine compound so that high heat resistance, high penetration in a visible ray range, excellent alignment capability, high voltage holding ratio, and a high vertical aligning force are assured, and a pretilt angle is easily controlled.
2. Description of the Related Art
Of LC alignment films for effectively aligning liquid crystal molecules, polyimide nicely endures high temperature treatment, and has excellent applicability, rubbability, chemical stability, and alignment controlling ability in comparison with other organic polymer compounds, thus it has been used for various LCDs. Generally, acid anhydride and a diamine compound react with each other in a solvent to produce polyamic acid, and polyamic acid is applied on a substrate, heated, and hardened to be imidized, thereby producing a polyimide-based LC alignment film.
In detail, a polyimide resin for an LC alignment film is produced by polycondensating monomers which are exemplified by aromatic acid dianhydride, such as pyromellitic dianhydride (PMDA) or biphthalic dianhydride (BPDA), and aromatic diamine, such as p-phenylene diamine (p-PDA), m-phenylene diamine (m-PDA), 4,4-methylene dianiline (MDA), 2,2-bis(aminophenyl)hexafluoropropane (HFDA), m-bis(aminophenoxy)diphenylsulfone (m-BAPS), p-bis(aminophenoxy)diphenylsulfone (p-BAPS), 4,4-bis(aminophenoxy)phenylpropane (BAPP), or 4,4-bis(aminophenoxy)phenylhexafluoropropane (HF-BAPP).
However, if only aromatic acid dianhydride and diamine are used as described above, thermal stability, resistance to chemicals, and mechanical properties are excellent, but, disadvantageously, transparency and solubility are reduced due to a charge transfer complex, and electrooptical characteristics are worsened.
Japanese Patent Laid-Open Publication No. Hei. 11-84391 suggests a process which employs an aliphatic cyclic acid dianhydride monomer or aliphatic cyclic diamine so as to avoid the above-mentioned problems. Japanese Patent Laid-Open Publication No. Hei. 6-136122 introduces functional diamine having side chains or functional acid dianhydride having side chains so as to increase the pretilt angle of liquid crystals and achieve stability. Furthermore, U.S. Pat. No. 5,420,233 discloses a vertical alignment-type aligning agent which consists essentially of polyimide having a linear alkyl group containing 12 or more carbons.
Recently, display performances of LCDs have been continuously improved, thus their application fields have expanded to PC monitors, mobile information terminals, large-sized televisions or the like. Accordingly, the demand for high quality LCDs is continuously growing. A wide viewing angle, high brightness, high contrast, and high speed response of the LCD must be assured in order to implement high quality large-sized LCDs. The demand for an LC alignment film having high productivity is growing as the trend toward large area LCDs is rapidly increasing. Hence, there is increased need to develop a high performance LC alignment film which has excellent processability and electrooptical properties and high reliability and which is capable of meeting recent requirements of the LCD. Particularly, a vertically aligned (VA) technology in which vertically aligned liquid crystals are used in a wide viewing angle LCD has been developed, thus there is a need to develop an LC alignment film which is capable of realizing vertical alignment.